User's Manual

11-7
Cisco IOS Software Configuration Guide for Cisco Aironet Access Points
OL-11350-01
Chapter 11 Configuring Authentication Types
Understanding Authentication Types
Figure 11-5 shows the reassociation process using CCKM.
Figure 11-5 Client Reassociation Using CCKM
Using WPA Key Management
Wi-Fi Protected Access is a standards-based, interoperable security enhancement that strongly increases
the level of data protection and access control for existing and future wireless LAN systems. It is derived
from and will be forward-compatible with the upcoming IEEE 802.11i standard. WPA leverages TKIP
(Temporal Key Integrity Protocol) for data protection and 802.1X for authenticated key management.
WPA key management supports two mutually exclusive management types: WPA and WPA-Pre-shared
key (WPA-PSK). Using WPA key management, clients and the authentication server authenticate to each
other using an EAP authentication method, and the client and server generate a pairwise master key
(PMK). Using WPA, the server generates the PMK dynamically and passes it to the access point. Using
WPA-PSK, however, you configure a pre-shared key on both the client and the access point, and that
pre-shared key is used as the PMK.
Note Unicast and multicast cipher suites advertised in WPA information element (and negotiated during
802.11 association) may potentially mismatch with the cipher suite supported in an explicitly assigned
VLAN. If the RADIUS server assigns a new vlan ID which uses a different cipher suite from the
previously negotiated cipher suite, there is no way for the access point and client to switch back to the
new cipher suite. Currently, the WPA and CCKM protocols does not allow the cipher suite to be changed
after the initial 802.11 cipher negotiation phase. In this scenario, the client device is disassociated from
the wireless LAN.
See the “Assigning Authentication Types to an SSID” section on page 11-10 for instructions on
configuring WPA key management on your access point.
88964
Reassociation request
Reassociation response
Pre-registration request
Pre-registration reply
Roaming client
device
Access point
WDS Device - Router/
Switch/AP
Authentication server
Wired LAN